Shaping of metal articles



March 0, 1956 J. 5. TURNBULL 2,733,571

SHAPING 0F METAL ARTICLES Filed March 24, 1955 2 Sheets-Sheet l INVENTOR ATTORN Mamh 1956 J. s. TURNBULL SHAPING 0F METAL ARTICLES 2 Sheets-Sheet 2 Filed March 24, 1955 \NVENT W Mimi M 'YMLW ATTORNEYS United States Patent SHAPING 0F METAL ARTICLES John Stratton Turnbull, Bowdon, England, assignor to Metropolitan-Vickers Electrical Company Limited, London, England, a company of Great Britain Application March 24, 1953, Serial No. 344,281 Claims priority, application Great Britain April 1, 1952 4 Claims. (Cl. 29156.8)

This invention relates to the shaping of metal articles or parts. An important application of the invention resides in the accurate shaping of component parts to desired form, such for instance as turbine and compressor blades, in an undertaking employing mass production methods of pressing a casting through the intermediary of a loose pad of material and in which the finished products are intended to conform to dimensions and shape which, due to unavoidable imperfections in the initial stages of manufacture, such for instance in casting, are not fully realised in practice.

In practising the lost-wax process of precision casting it frequently happens that the resulting castings are not true to the shape intended but are to some extent distorted, such distortion usually being manifest in the form of surface excrescences and hollows, being mainly due to stresses set up in the casting metal while it is cooling to room temperature or to the restriction of movement in the mould while the casting is contracting; distortion may also be produced during any subsequent heat treatment to which the casting may be subjected after it has been knocked out of the mould.

Usually the effect of the distortion is that the casting must be reshaped so as to conform to the shape originally intended. This reshaping will generally involve manipulation by skilled laboura factor which, especially in the case of an undertaking using mass-production methods for obtaining the parts of desired accurate shape, may impose undesirable restrictions on production.

This invention has for an object to provide a simple, speedy and economical method whereby metal parts can be brought to desired accurate predetermined shape.

In a method according to the invention of shaping accurately a face of a metal part or article, the face to be shaped is arranged to be pressed against a die surface conforming to the desired shape by means of a pad of material which is capable under pressure of assuming a condition of plastic deformation or flow so as to result in substantially uniform pressure distribution whereby to cause the face to be shaped intimately to engage and conform with the shape of the die surface.

In a method according to the invention of shaping accurately a face of a metal part or article, the face to be shaped is arranged to be pressed against a die surface conforming to the desired shape by means of a pad of material which is capable under pressure of assuming a condition of plastic deformation or flow so as to result in substantially uniform pressure distribution whereby to cause the face to be shaped intimately to engage and conform with the shape of the die surface.

In practising the invention it is generally preferable to press the pad of deformable material against a face of the article or part by a die surface corresponding approximately in shape to said face. The degree of divergence of form allowable between the pressing die surface and the face of the article or part is proportional to the thickness of the deformable pad to be disposed therebetween. For example an asbestos pad one sixteenth of an inch thick can absorb disconformities of up to 0.005 inch whereas an for the errors contained in the other face to be removed by more usual methods such as by grinding and/ or polishing.

As regards the application of the invention in respect to turbine and compressor blades, it is recognised that for compressor blades the concave form is much more difiicult to grind or polish owing to the necessity for using small diameter grinding or polishing wheels and accordingly it is contemplated to apply the invention for the accurate shaping of the concave form of the compressor blades and to correct any residual errors in the convex form by polishing or grinding namely in respect of which the use of large diameter polishing or grinding wheels is possible; in the case of turbine blades, for which the convex form is the more important, the convex form would be pressed accurately to shape according to the invention and any necessary corrections to form made on the concave face. I

In carrying out the invention, the deformable material used during the pressing operation, namely as the pressure distributing medium, may vary according to circumstances. Thus, in. the case of relatively highly-ductile parts, that is parts which can be pressed to accurate shape when cold, such for instance as turbine blades made of austenitic steel, the deformable material could be rubber; the shaping of other parts may require the application of heat as for instance in the case of compressor blades which, being made of high-tensile, low-ductility steel, require to be heated to a temperature of the order of 650 C. and for these parts, rubber being impracticable, the material may conveniently be asbestos.

The thickness of the pad of deformable material should be adequate for the purposeit would depend on such factors as the extent of the distortion to be corrected; in cases where little distortion is present, a thickness of oneeighth to one-sixteenth of an inch may suflice; in more severe cases of distortion, a thickness of the order of half an inch may be practical.

After the rubber, asbestos, or other deformable pressure distributing medium has once been used for a pressing operation .and has thus been brought to the state of plastic flow, it will generally be desirable to discard it since if used again the best results are not be be expected.

Advantageously, the rubber, asbestos or like material should be treated with suitable lubricant to prevent its adhesion to the part being shaped or the die; in the case of asbestos, a suitable lubricant is graphite and white spirit.

It is contemplated to employ a relatively high pressure, such as of the order of tons per square inch in the case of compressor and turbine blades in which surface imperfections in the form of excrescences or hollows of a height or depth in the order of :0.003 inch are likely to be present, with a view to minimising the efiect of springback after removal of the pressure.

The operation of shaping may be carried out in closed or open dies according to circumstances.

One embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a pictorial view of a press tool according to the invention as applied in respect of compressor blades of high-tensile, low-ductile steel, and

Fig. 2 is a side elevation of the press tool shown in Fig. 1.

The press tool shown in the drawings comprises a bottom die I mounted on a bottom plate 1' and, a top die 2 mounted beneath a top plate 2' which is conveniently located by means of location pillars 3 over which bushes 3 in the plate 2 slide when the top plate is pressed. downward. Springs 4 (Fig. 2) keep the two dies spaced apart when no pressure is being exerted.

The bottom die 1 has an accurate convex face 5 corresponding to the accurate shape desired for the concave face 6 of. the blade 7.

A block 8 is attached to a side face of the bottom die 1 for example by means of screws 9 (Fig. 1)., the block being provided with a plunger 10 which slides in the block 8 and in a semi-circular section groove 11 in the bottom die. The end of the plunger remote from the die projects through the block and engages a spring finger 12, held on the block by a screw 13, which finger urges the plunger inwardly of the die to hold the blade against two pins 14 which are accurately positioned in the bottom die so as to locate the blade in its correct position. A semi-circular groove 11 corresponding to the plunger is also provided in the top die in order to accommodate the plunger when the dies are pressed together. The press tool is set up on a press capable of delivering a pressure of say 50 tons per square inch. After the compressor blade 7 is heated to a suitable temperature, say 650 C., it is placed in the press tool with its concave face 6 resting on the convex surface 5 of the bottom die 1 and the plunger 10 holding it against the pins 14. A pad 15 of asbestos of suitable thickness and preferably covered by graphite and white spirit as lubricant, is then placed over the blade and the press is operated to deliver pressure through the top die. 2 and the asbestos pad 15 onto the blade. It is envisaged that pressure will be applied for a period of ten seconds or so. During increase of the pressure to its maximum value of 50 tons per square inch or so, the asbestos becomes compressed and then assumes a state of plastic deformation or flow, whereupon the pressure will be caused to be distributed evenly over the Whole surface of the blade in contact with the top die. In the result, and with the temperature and timing suitably selected, the underface of the blade will be caused accurately to. conform with the shape of the bottom die, a condition in which all errors are contained in the upper face of the blade. This upper face being convex, the residual errors can be corrected by more orthodox methods of polishing and/or grinding.

What I claim is:

1. The method of forging a turbine type blade casting to produce accurate shaping of a face thereof to a predetermined form, which consists in forcing the blade casting, While it is at a temperature appreciably less than its melting point and with said face engaged against a die surface conforming to the predetermined form, by the application of pressure at the opposite face of said blade casting through the intermediary of a loose pad of material capable under the applied pressure of plastic flow without application of heat so as to result in substantiallyuniform pressure distribution on the blade casting acting to intimately engage the face to be accurately shaped against the die surface of predetermined form and to cause transfor of errors from said face to the opposite face.

2. The method as defined in claim 1, wherein said. pad is made of asbestos, and the pressing is performed at a raised temperature below the fusion temperature of the blade casting.

3. The method as defined in claim 2, wherein said pad is covered with a suspension of graphite in white spirit to act as a lubricant and prevent adhesion of the pad to the blade casting.

4. The method as defined in claim 1, wherein said pad is made of rubber, and the pressing is performed at relatively low temperature.

References (Iited in the file of this patent UNITED STATES PATENTS 1,771,368 Allen July 22, 1930 1,772,600 Dorman Aug. 12, 1930 2,276,035 Guhl Mar. 10, 1942 2,384,349 Sherman Sept. 4, 1945 2,430,083 Sherman Nov; 4, 1947 2,538,917 Sejournet et al Jan. 23, 1951 FOREIGN PATENTS 1,073 Great Britain 1913 333,871 Great Britain Aug. 19, 1930 716,480 Germany Jan. 21, 1942 655,743 Great Britain Aug. 1, 1951 

1. THE METHOD OF FORGING A TURBINE TYPE BLADE CASTING TO PRODUCE ACCURATE SHAPING OF A FACE THEREOF TO A PREDETERMINED FORM, WHICH CONSISTS IN FORCING THE BLADE CASTING, WHILE IT IS AT A TEMPERATURE APPRECIABLY LESS THAN ITS MELTING POINT AND WITH SAID FACE ENGAGED AGAINST A DIE SURFACE CONFORMING TO THE PREDETERMINED FORM, BY THE APPLICATION OF PRESSURE AT THE OPPOSITE FACE OF SAID BLADE CASTING THROUGH THE INTERMEDIARY OF A LOOSE PAD OF MATERIAL CAPABLE UNDER THE APPLIED PRESSURE OF PLASTIC FLOW WITHOUT APPLICATION OF HEAT SO AS TO RESULT IN SUBSTANTIALLY UNIFORM PRESSURE DISTRIBUTION ON THE BLADE CASTING ACTING TO INTIMATELY ENGAGE THE FACE TO BE ACCURATELY SHAPED AGAINST THE DIE SURFACE OF PREDETERMINED FORM AND TO CAUSE TRANSFER OF ERRORS FROM SAID FACE TO THE OPPOSITE FACE. 